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[Neale Upstone <1516370@xxxxxxxxxxxxxxxxxx>]

For anyone interested in the intel backlight.  That still doesn't work
on 4.3 either, but I've not dug into that.

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https://bugs.launchpad.net/bugs/1516370

Title:
  Vendor backlight on Lenovo Z580 having random hotkeys issues

Status in linux package in Ubuntu:
  Confirmed

Bug description:
  I've taken a bold guess in the title of this bug.

  While investigating why on 14.04 LTS, I have working backlight on the
  latest 3.13 kernel, but not on the 3.16, I tried
  acpi_backlight=vendor.

  With default boot parameters, I just get
  /sys/class/backlight/intel_backlight/, and the backlight works
  correctly on 3.13, but does not change the brightness on 3.16 (the OSD
  does show that the hotkeys are trying to change the brightness).

  With acpi_backlight=vendor, I get both intel and /lenovo/.

  The key point for this bug report is what happens with the lenovo one:

  The hotkeys work and make the backlight change, but not consistently.
  Repeatedly using the hotkey to increase the brightness causes the
  level to increase, but then occasionally reset to zero (including
  resetting as shown in the OSD - i.e. the OSD is always showing the
  level that the backlight actually is).

  Occasionally the OSD shows the "enable touchpad" icon when pressing
  the increase brightness hotkey repeatedly.  The same action also
  causes the wifi to enable/disable randomly.

  If I press the hotkey with pauses in between, things behave normally.

  ProblemType: Bug
  DistroRelease: Ubuntu 14.04
  Package: linux-image-3.13.0-67-generic 3.13.0-67.110
  ProcVersionSignature: Ubuntu 3.13.0-67.110-generic 3.13.11-ckt27
  Uname: Linux 3.13.0-67-generic x86_64
  NonfreeKernelModules: nvidia
  ApportVersion: 2.14.1-0ubuntu3.18
  Architecture: amd64
  AudioDevicesInUse:
   USER        PID ACCESS COMMAND
   /dev/snd/controlC0:  neale      3106 F.... pulseaudio
  CurrentDesktop: Unity
  Date: Sun Nov 15 11:16:55 2015
  HibernationDevice: RESUME=UUID=1fd50851-1727-4432-a99c-d0be8aafc983
  InstallationDate: Installed on 2013-10-23 (752 days ago)
  InstallationMedia: Ubuntu 13.10 "Saucy Salamander" - Release amd64 (20131016.1)
  MachineType: LENOVO IdeaPad Z580
  ProcFB: 0 inteldrmfb
  ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-3.13.0-67-generic root=UUID=d66417de-a540-485b-b469-aabd51a8844b ro quiet splash acpi_backlight=vendor
  RelatedPackageVersions:
   linux-restricted-modules-3.13.0-67-generic N/A
   linux-backports-modules-3.13.0-67-generic  N/A
   linux-firmware                             1.127.18
  SourcePackage: linux
  StagingDrivers: rts5139
  UpgradeStatus: Upgraded to trusty on 2014-03-17 (607 days ago)
  dmi.bios.date: 12/25/2012
  dmi.bios.vendor: Phoenix Technologies Ltd.
  dmi.bios.version: 5FCN95WW
  dmi.board.asset.tag: No Asset Tag
  dmi.board.name: Lenovo
  dmi.board.vendor: LENOVO
  dmi.board.version: 31900003WIN8 STD MLT
  dmi.chassis.asset.tag: No Asset Tag
  dmi.chassis.type: 10
  dmi.chassis.vendor: LENOVO
  dmi.chassis.version: Lenovo Z580
  dmi.modalias: dmi:bvnPhoenixTechnologiesLtd.:bvr5FCN95WW:bd12/25/2012:svnLENOVO:pnIdeaPadZ580:pvrLenovoZ580:rvnLENOVO:rnLenovo:rvr31900003WIN8STDMLT:cvnLENOVO:ct10:cvrLenovoZ580:
  dmi.product.name: IdeaPad Z580
  dmi.product.version: Lenovo Z580
  dmi.sys.vendor: LENOVO

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